Vitamin K Interactions

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Vitamin K has interactions with other substances, including:

Antacids
People taking antacids, especially if they have been taking them long term may become deficient in vitamin K because the antacids block absorption and also effectiveness of vitamin K.
Antibiotics
People taking antibiotics may easily become deficient in vitamin K because the antibiotics destroy the very bacteria that would normally be creating the vitamin K in the intestines.
Anticoagulants
People taking any type of anticoagulant medications, which are used to stop the blood from clotting (they are used in people who have an existing blood clot which needs to be broken up and disintegrated before it can travel to the heart or brain and cause heart attack or stroke), should not take any vitamin K supplements as this combination can thin the blood too much and cause internal bleeding which may not be able to clot properly and may not stop bleeding. People taking these medications should also not eat foods rich in vitamin K either.
Blood thinners (Coumarin, Coumadin, Warfarin)
People taking any type of blood thinning medications such as Coumarin, coumadin or warfarin to break up blood clots, should not take any vitamin K supplements as this combination can thin the blood too much and cause internal bleeding which may not be able to clot properly and may not stop bleeding. People taking these medications should also not eat foods rich in vitamin K either.
Cholestyramine and Colestipol
People taking cholestyramine for decreasing LDL ("bad") cholesterol levels may have decreased vitamin K levels as this drug blocks absorption and effectiveness of vitamin K from foods eaten, so supplementation may be required.
Dactinomycin
People taking dactinomycin, an anti-cancer chemotherapy medication may have decreased vitamin K levels as this drug blocks absorption and effectiveness of vitamin K from foods eaten, so supplementation may be required.
Haemolytics
People taking haemolytics should not take vitamin K supplements at the same time, as this combination can increase the potential for toxicity symptoms due to much higher than normal vitamin K levels.
Primaquine
People taking primaquine, a medication to treat malaria should not take vitamin K supplements at the same time, as this combination can increase the potential for toxicity symptoms due to much higher than normal vitamin K levels.
Quinidine
People taking quinidine, a medication to treat abnormal heart beat (arrhythmia) may have very decreased vitamin K levels and even a deficiency, as this drug really blocks absorption and effectiveness of vitamin K from foods eaten, so supplementation will usually be required.
Salicylates
People taking salicylates, which are anti-inflammatory medications that reduce pain and fever, over a long term may need vitamin K supplementation as these drugs cause decreased levels of vitamin K.
Sucralfate
People taking sucralfate for reducing symptoms associated with ulcers and gastritis may have decreased vitamin K levels as this drug blocks absorption and effectiveness of vitamin K from foods eaten, so supplementation may be required.
Sulfa drugs
People taking sulfa drugs, which are antibiotics used to treat bacterial infections, may experience low levels of vitamin K and supplementation will normally be needed to prevent deficiency symptoms.